Tests in in vitro diagnostics can have several assay formats. Cluster assays are a class of assays in which the amount of formed particle clusters is indicative of the presence and/or concentration of biological components in the sample. Cluster assays are attractive because of the rapid bulk kinetics, ease of fabrication and low costs.
The main issue with cluster assays is the lack of sensitivity. One way to improve the sensitivity is by performing cluster assays with magnetic particles. An advantage of using magnetic particles is that field-induced chains can be formed during incubation. This has, e.g., been shown by Baudry et al. “Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces”, Proc. Natl. Acad. Sci. p. 16076).
One important challenge when performing cluster assays is to detect very low concentrations of clusters in a background of other magnetic particles. Another challenge is to avoid the formation of clusters of non-biological origin, and preferably to even break weakly bound clusters. These challenges are particularly important when magnetic actuation is used during the detection.